Overheating after freshwater conversion

I spoke to my mechanic and we're going to install a thru-hull raw water pickup. This will remove any possibility of a restriction of flow via the outdrive as described by Chris earlier in this thread. For peace of mind I'm having them install a drive shower too.

I can also justify this expense just for getting in and out of my marina as it will reduce the chance of sucking in mud and seaweed at low tide near the entrance. As it turns out my mechanic just did this for the marina’s owner too (thru-hull and shower), he has a ‘04 260 Weekender.

I’ll keep you posted, but please keep the ideas coming.

Thank you!
 
I think the shower is a bit of "over kill" on a Bravo drive. If you see the internal castings of a Bravo, there is a large chamber of water around the top gear box, and while the drive / boat is travelling through the water, there is a large quantity of water flowing through it.

Actually, the shower is only cooling the outer wall of the internal water jacket ! If you were driving and Alpha with a 377cid (6.2L) or a 454, then a shower would be recommended. The water flow through a Alpha drive is completely different having the raw water pump in the lower gear box.

The most important thing on the Bravo drives, is to cut the section out of the hose to the transom plate when you go to through the hull cooling.
 
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Did you read what I posted?
You'd be doing yourself a favor by telling your mechanic about my experience and resolution.
 
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magster65 said:
Did you read what I posted?
You'd be doing yourself a favor by telling your mechanic about my experience and resolution.
Click to expand...

Magster65,

Yes I did, did you see my reply? Did you install a Monitor heat exchanger? If so what model? I did tell my Mechanic about your experience too. I hope that's all it is.
 
Hornblower said:
Magster65,

Yes I did, did you see my reply? Did you install a Monitor heat exchanger? If so what model? I did tell my Mechanic about your experience too. I hope that's all it is.
Click to expand...

What the heck? I see your reply now... I don't know how I missed it earlier! :smt101
Mine was a 'San Juan Manufacturing' kit.
So I looked through your install guide and see it has fittings for the sensors where they should be... so your problem is different :smt009
Drats... thought we had it there.
The symptoms are the same though...
I'm sure the through-hulls are gonna' solve your problem.
 
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SCORPIO said:
How much pressure are you running in the system?
Click to expand...

I took the boat out Sunday (8/22) for a short spin (all I can really do right now). It’s the second time running with the bypass flow reducer installed that Monitor Products (heat exchanger manufacture) sent me (see details early on in this thread), and wanted to collect more data on how the temp behaves with it, and prior to the raw water thru-hull is installed.

I warmed up the engine to about 150deg and headed out of the marina. As it was very low tide I didn't open her up till I was near the channel about a 10 min ride at 2000RPMish, and the temp stayed at 154deg with a bay water temp of 74deg. I jumped up on plane and settled in at 3800RPM. The engine temp kept climbing, but slowed down as it hit the low 180’s. At 184deg after about 7 min, I could tell as before it wasn’t done heating up. I didn’t want to wait for the temp to get any higher so I slowly pulled back the throttle; first to 3000 then 2500, it held on to 184deg for what seemed like a couple of minutes and then it finally dropped to 174deg. At that point I know I had it under control and could reduce to idle speed. If I had dropped down to anything near idle speed the temp would’ve shot right past the195deg overheat alarm threshold.

My mechanic is installing the thru hulls this week. After he does, I’m going to take it out and pretty much run the same test as above.

The silver lining is that one of our favorite anchorages is close by, so after the quick test and of jotting notes we putted over to it, dropped a hook and enjoyed the afternoon.

For what it’s worth and because SCORPIO asked, I took some water pressure readings while I was at it:
RPM Water Pressure
600 12.2
1330 23.9
2000 32.8
3800 40.7
 
magster65 said:
When do you get your boat back?
Click to expand...

The plan is for the thru-hull to be put in and tested during the week so I can have the boat back for the weekend. Not that I'll be able to go very far it doesn't improve the situation.

Also I just spoke to my customer service contact James at Monitor Products who just got back from vacation. He tells me he will talk to their engineer about my situation again and will call me back with further recommendations tomorrow afternoon.

I’ll keep you posted.
 
Yeah I'm curious now... thanks :thumbsup:
It's unfortunate to have trouble but it's nice that the manufacturer hasn't 'split town'!
Sounds like they're still with ya' :smt038
 
It sounds like the heat exchanger isn't big enough for the 350 Mag. Not enough coolant capacity or heat transfer from raw. I bet if you took the manifolds out of the coolant circuit all your problems will go away...
 
Nah, I don't think so Mike, my heat exchanger was for my 350 and now it's a 383 stroker with a performance cam and cylinder heads, pulling 400 HP when we dyno tuned it.

A lot more heat now and I have the manifolds plus the 3 inch risers in the fresh water circuit and she never goes over 170F even at WOT.

Also, I'm tropical Queensland and the sea temperature never goes much below 24C.

The best part of having FWC is to protect those manifolds. :thumbsup:
 
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Here’s something else to chew on, my mechanic found that Mercruiser offers an alternate water pump pulley for FWC engines (different belt too), part no. 865047T PULLEY Water Pump (Closed Cooling).

Is anyone familiar with it?

My guess is it is a smaller pulley so the circulator spins a little faster, but I haven’t been able to confirm.

It’s not cheap at $113 vs. $31 for the standard pulley.

http://www.mercurypartsexpress.com/us/parts-search.html#mr1153ar5315
 
Hornblower said:
Here’s something else to chew on, my mechanic found that Mercruiser offers an alternate water pump pulley for FWC engines (different belt too), part no. 865047T PULLEY Water Pump (Closed Cooling).

Is anyone familiar with it?

My guess is it is a smaller pulley so the circulator spins a little faster, but I haven’t been able to confirm.

It’s not cheap at $113 vs. $31 for the standard pulley.

http://www.mercurypartsexpress.com/us/parts-search.html#mr1153ar5315
Click to expand...


That is very interesting, but is makes sense... Since you have a heat transfer loss at both the HE and the engine, you would need to speed up the water flow to increase the heat transfer rate. A smaller pulley would make the pump spin faster and you would get more flow through the HE... that might solve your problem...
 
I wound up calling Monitor Products yesterday afternoon as they didn’t call me back.

I explained that I’m adding a thru-hull and they agree that it is a good thing. The customer service rep I’ve been dealing with there James says the raw water pump is high pressure but low volume and hinting that it’s just enough to do the job. He also says that the flow on the raw water side is most important.

As you may already know water moves heat better than coolant. As described earlier in this thread I went from near 100% Prestone, to premixed 50/50 Shell Rotella antifreeze. James said that 1/3 antifreeze would be even better and would still be enough to protect the engine.

Here’s what James said I should test:

1) Test the raw water temp with an IR gun by checking the temp of the exhaust elbow. It should read 110 deg, if it’s hotter, there’s not enough raw water flow.

2) Test the raw water flow by disconnecting the hose from the heat exchanger raw water intake and measure the volume into a 5 Gal pail at idle. When the bucket fills up, check the time and do some math (ex. 5gal in 20 sec = 15 gal/min). He says it should be 15 to 20 gal a min. I bet that one of you would have a more accurate figure.

3) Check/verify the temp gauge/sensor by testing the temp at the lower heat exchanger bracket (where the sensor/sender is located).

I hope that the thru-hull will be completed today (had a shipping SNAFU with the part); if not or if it doesn’t improve the situation, I’m going to see if I can’t get my mechanic with is IR Gun on board for a spin and do some testing tomorrow morning.
 
I thought about adding this to my boat but now it just doesn't seem worth it. I'll continue to flush my drives/motors every time I take her out.
 
My mechanic just called, he took the boat out this morning to do some testing and take some temperature readings.

With the boat on a plane and the temp at 180 and rising, the exhaust elbows were 110 deg, right where they should be.

They also disconnected a hose to visually see raw water flow and said it was coming out like a fire hose.

Also the gauge on the dash matched the temp at the heat sensor.

I spoke to him yesterday evening too and he told me that he had checked the thru transom fitting for the raw water pickup in the beginning of the season. He has seen the constricting issue as described by others earlier in this thread. He say that it’s mine has no issues.

So he didn't put the thru-hull in yet because he wanted to do this testing first, and from what he found it appears that it wouldn’t make a difference, as the raw water side checks out. Good flow and the raw water temp exiting at the elbow are in range.

So if it’s not the raw water side it must be the freshwater side, right?

While my mechanic is working on it, do you have any thoughts or ideas? :huh:
 
You mean suggestions other than pulling that system off and going boating? The boat is six years old. Installing closed cooling is darned near pointless. The only good it's doing is keeping you from wasting a lot of gas by going for boat rides the past few weekends.
 
Dave S said:
Have you tested the temperature of the heat exchanger itself with the IR gun?

Dave
Click to expand...

Yes they did. The ends were cool (that's normal) the center was hot, particularly where the freshwater dumps into the exchanger from the engine. I don't recall him mentioning to me the actual temp readings on the exchanger.
 
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